Exploring ancient worlds and the plants and animals that lived in them

Monday, September 10, 2012

OUT ON THE TOWN WITH FOSSILS

Fossils can be frustratingly, even maddeningly, rare, especially those of vertebrates. Invertebrates, including the hard parts of single cell organisms, can sometimes be so abundant as to make up nearly all of the composition of a rock. Since some types of rocks are used in buildings it's not surprising that fossils sometimes show up in very public places. One only needs to look for them to see them.

The use of limestone as a decorative building stone often results in abundant fossils that most people simply walk past without ever noticing. The newly opened City Creek Mall in Salt Lake City, with many highly polished slabs of Mesozoic limestone lining its stairways and escalators, is a fine example of this.

The pen shaped internal skeleton of a squid-like
belemnite, City Creek Mall. In the living animal the head and tentacles
would be on the right.

I've even seen cross sections of fossils shells in the limestone partitions in men's rooms stalls. I had more pressing concerns on my mind at the time and didn't think of taking my camera with me into the bathroom, so sorry no photos.

The sandstone of the 190,000,000 Early Jurassic Nugget Sandstone is a common building stone in Salt Lake City and environs. This rock, formed by a vast sand dune desert that covered most of the intermountain west at that time, can be nicely split and used as paving stones. If you keep your eyes open, you might catch something like this....

An ancient scorpion trail in a stone stairway made of slabs of Nugget Sandstone, undisclosed site. Each circular pit is a leg
impression. Direction of travel is to the right.

Three footprints made by a long extinct reptile walking
up the front slope of a dune in the Nugget Sandstone, undisclosed site.
Note the clear toe impressions in the upper track.

Nugget walkway slabs are also sold to the public. Lowe's carries large numbers of them in our area and I've often stopped to take a quick peek at the piles. Good thing too, because one day there was a single slab with hand and foot impressions of a reptile that walked across these ancient dunes eons ago. For $6.95 it was mine.

Homeowners pile up rocks on their property to form walls, for decorative purposes, or just to get them out of the way. This ring of rocks around the base of a tree on a front lawn shows fragmentary remains of Cretaceous plant foliage.

However, one cannot always believe one's eyes. You need to be alert for pseudofossils --- features, shapes, etc. that look like a fossil but are of inorganic origin. The example below is one of the pillars on the front of the Utah State Capitol building. The pillar, as most of the buildings at the Capitol, is granite, a volcanic rock that forms from the solidification of molten rock in ancient magma chambers. Jellyfish are remarkable for sure, living in environments ranging from the cold waters of the polar regions to the warm waters of the tropics, in fresh water and salt water, and from sunny surface waters to the deepest parts of the ocean in excess of 30,000 feet. Yet no jellyfish are known to live in magma chambers. The dark shape is a natural curiosity of dark mafic minerals that crystallized into a shape that the human visual system and memory interprets as a jellyfish.

At the County Court House in Vernal, Utah there's a plaque mounted on a block of Cretaceous Frontier Sandstone However, on the backside of the block there's more interesting reading. Hidden behind a tall patch of flowers is the impression of a fairly large Cretaceous ammonite mollusk.

Memorial plaque celebrating Utah's statehood centennial, Vernal.

The more interesting back side of the memorial block, with the impression of a spiral ammonite shell.

And speaking of fossil impressions, one of my earliest fossil memories is that of a stone shed on my grandmother's property in New Jersey. It was built of stones rounded by tumbling for millennia in river beds . Of the hundreds of stones cemented in its walls, one cobble bore the distinct impression of a small brachiopod. When the gaze of my young eyes first fell upon this fossil it seemed as amazing as any treasure of ancient Egypt. How no one had seemed to notice it was beyond me. Even more puzzling was everyone's apparent lack of interest even after it was pointed out to them. For some inexplicable reason they wouldn't let me take a hammer and bash it out. I suppose they didn't want me to damage the wall. Besides, they were sure that I would soon certainly grow out of my childish mania about fossil. HA-HA, the joke was on them!

PHOTOS

All photos by the author, with the exception of the reptile tracks from an undisclosed site which is courtesy of Brian Switek..

About Me

DAN CHURE:
I have been the paleontologist at Dinosaur National Monument for 34 years. My main research interests are dinosaurs & the ecosystems they lived in. I am also interested in fossil resource management & preservation, & the impacts of 20th century warfare and social revolutions on fossil collections & scientists. This blog is personal and not an official blog of Dinosaur National Monument or the National Park Service.